Your problem is that when you read in from the keyboard you get the "\n" (newline) as well. You can chomp that variable in yourcase $usersex, like chomp $usersex and it should work.
To clarify what vroom has said, change your lines so that where you are asking for input you have (for example):chomp ($usersex = <STDIN>);This will also prevent the output looking like this:
setantae
is 23
years old and lives in Wales
In a year will be 24 setantae
is a boy
$userboy will still show up as nothing unless the user enters exactlyboy or girl. You may also want to check for more common user input, such as b, g, Boy, BOY, etc.